Do not use the fstab parameter on openbsd for mounting (#5805)

* Do not use the fstab parameter on openbsd for mounting

OpenBSD's mount command doesn't allow selecting which fstab file to use.
So if we're operating on the live filesystem (mount or remount) return
an error if the user specified an fstab file.

Fixes #5591

* Fix the logic inversion (thanks to @landryb)

lib/ansible/modules/system/mount.py

@@ -90,9 +90,11 @@ options:
     choices: ["present", "absent", "mounted", "unmounted"]
   fstab:
     description:
-      - File to use instead of C(/etc/fstab). You shouldn't use that option
+      - File to use instead of C(/etc/fstab). You shouldn't use this option
         unless you really know what you are doing. This might be useful if
-        you need to configure mountpoints in a chroot environment.
+        you need to configure mountpoints in a chroot environment.  OpenBSD
+        does not allow specifying alternate fstab files with mount so do not
+        use this on OpenBSD with any state that operates on the live filesystem.
     required: false
     default: /etc/fstab (/etc/vfstab on Solaris)
   boot:
@@ -308,14 +310,14 @@ def unset_mount(module, args):
 
     return (args['name'], changed)
 
-def _set_fstab_args(args):
+def _set_fstab_args(fstab_file):
     result = []
-    if 'fstab' in args and args['fstab'] != '/etc/fstab':
+    if fstab_file and fstab_file != '/etc/fstab':
         if get_platform().lower().endswith('bsd'):
             result.append('-F')
         else:
             result.append('-T')
-        result.append(args['fstab'])
+        result.append(fstab_file)
     return result
 
 def mount(module, args):
@@ -328,7 +330,13 @@ def mount(module, args):
     if ismount(name):
         return remount(module, mount_bin, args)
 
-    cmd += _set_fstab_args(args)
+    if get_platform().lower() == 'openbsd':
+        # Use module.params['fstab'] here as args['fstab'] has been set to the
+        # default value.
+        if module.params['fstab'] is not None:
+            module.fail_json(msg='OpenBSD does not support alternate fstab files.  Do not specify the fstab parameter for OpenBSD hosts')
+    else:
+        cmd += _set_fstab_args(args['fstab'])
 
     cmd += [name]
 
@@ -364,7 +372,13 @@ def remount(module, mount_bin, args):
     else:
         cmd += ['-o', 'remount' ]
 
-    cmd += _set_fstab_args(args)
+    if get_platform().lower() == 'openbsd':
+        # Use module.params['fstab'] here as args['fstab'] has been set to the
+        # default value.
+        if module.params['fstab'] is not None:
+            module.fail_json(msg='OpenBSD does not support alternate fstab files.  Do not specify the fstab parameter for OpenBSD hosts')
+    else:
+        cmd += _set_fstab_args(args['fstab'])
     cmd += [ args['name'], ]
     out = err = ''
     try:
@@ -564,7 +578,7 @@ def main():
         argument_spec=dict(
             boot=dict(default='yes', choices=['yes', 'no']),
             dump=dict(),
-            fstab=dict(default='/etc/fstab'),
+            fstab=dict(default=None),
             fstype=dict(),
             name=dict(required=True, type='path'),
             opts=dict(),
@@ -586,26 +600,32 @@ def main():
     #   name, src, fstype, opts, boot, passno, state, fstab=/etc/vfstab
     # linux args:
     #   name, src, fstype, opts, dump, passno, state, fstab=/etc/fstab
-    if get_platform() == 'SunOS':
+    # Note: Do not modify module.params['fstab'] as we need to know if the user
+    # explicitly specified it in mount() and remount()
+    if get_platform().lower() == 'sunos':
         args = dict(
             name=module.params['name'],
             opts='-',
             passno='-',
-            fstab='/etc/vfstab',
+            fstab=module.params['fstab'],
             boot='yes'
         )
+        if args['fstab'] is None:
+            args['fstab'] = '/etc/vfstab'
     else:
         args = dict(
             name=module.params['name'],
             opts='defaults',
             dump='0',
             passno='0',
-            fstab='/etc/fstab'
+            fstab=module.params['fstab']
         )
+        if args['fstab'] is None:
+            args['fstab'] = '/etc/fstab'
 
-    # FreeBSD doesn't have any 'default' so set 'rw' instead
-    if get_platform() == 'FreeBSD':
-        args['opts'] = 'rw'
+        # FreeBSD doesn't have any 'default' so set 'rw' instead
+        if get_platform() == 'FreeBSD':
+            args['opts'] = 'rw'
 
     linux_mounts = []
 
@@ -624,9 +644,6 @@ def main():
         if module.params[key] is not None:
             args[key] = module.params[key]
 
-    if get_platform() == 'SunOS' and args['fstab'] == '/etc/fstab':
-        args['fstab'] = '/etc/vfstab'
-
     # If fstab file does not exist, we first need to create it. This mainly
     # happens when fstab option is passed to the module.
     if not os.path.exists(args['fstab']):